D. Reduce Anonymity
According to John Gabriel's Greater Internet F****** Theory, the combination of anonymity and an audience causes normal people to feel free to act badly. So maybe reducing anonymity is a valid strategy to build a better community.
6. Tie all characters to a single id
Remove the idea of anonymous alts. All alts can be identified as belonging to the same player/account.
7. Tie all accounts to real word name or identity
This takes the previous idea a step further. Your online identity is linked to your real name.
In addition to reducing the anonymity of the would-be bad actor, this also might have the additional effect of "humanizing" the other players. Sometimes when you're playing with a bunch of avatars, it's easy to dehumanize them and treat them as effective NPCs. Perhaps using real names will remind people that they are playing with real people.
I also want to respond to a couple of specific comments made.
Community Based Policing
Isn't the central problem: "The Internet is a horrible place to have a community"? The only working solution on a fairly large scale tends to be a strong, user community based policing.
I am not as sure of this as you are. Community based policing enforces the current norms of the community. So if the community is bad, the norms it enforces will be bad as well.
For example, if you picked 5 random WoW players and presented them with one player, Sue, who used the word "gay" as a pejorative, and other player, Jane, who does 2K dps in heroics, who do you think the community is more likely to censure?
(If you say Sue, I have a bridge in Brooklyn that you might be interested in.)
In my experience, community based policing only really works when the power is not given to the community at large, but to a subset of users who have a vision of what the community should be. Often older or original members of the community.
As well, community based policing is vulnerable to hijack by organized "mafias". A small group working together can often intentionally push the community moderation in an unintended direction. Just imagine if Goonswarm gets to be the police in your MMO community.
Moderated Servers and the Best Guilds
Create specific servers where there is little to no moderation or banning and see where people choose to roll their mains. Five bucks says that many who try out the "freedom of speech" servers will realize society without laws isn't as peachy as they thought, and that a little (self) moderation goes a long way in improving play experience. I wouldn't be surprised at all to see the best guilds thrive on the moderated servers.
This might or might not be a good idea. But personally, I would be shocked if the best guilds were on moderated servers.
The best players tend to come from the young, male, hyper-competitive gaming culture.1 Killer-Achievers, basically. They are not particularly attracted to moderated servers. The culture is often crass, and contains a lot of bravado. They're not bad, per se. If the lines are laid down, they will stay more or less within them, pushing the edges where they can.
But that culture would see it as a point of pride to be top dogs on the non-moderated servers. A sort of "if you can't stand the heat, get out of the kitchen" attitude.
1. I'm not saying that they're all male, or all young, but the core of most high end guilds tend to be males in their 20s.